Recent literature has indicated that there exists a trade-off in information and power flow and that intelligent, coordinated control of power flow in a microgrid system can modify energy storage hardware requirements. The future electric power grid and corresponding microgrid systems will require new mathematical tools and methodologies to support high penetration of renewable energy sources such as solar and wind and provide specific optimized designs. Current unidirectional power flow from source to load will be replaced by bi-directional power flow as new generation sources are being distributed onto the future electric power grid. Renewable and other distributed energy sources cannot be economically and reliably integrated into the existing grid because it has been optimized over decades to support large centralized generation sources.
A recent review focused on hierarchical controls covering three main levels and identified that future control trends needed further research in interconnected microgrids. See E. Unamuno and J. A. Barrera, Renew. Sust. Energy Rev. 52, 1123 (2015). The problems and solutions of power quality in microgrids, distributed-energy storage systems, and hybrid AC/DC microgrids, including power quality enhancement, cooperative control for voltage enhancement, harmonics, and unbalances in microgrids have also been reviewed. See J. M. Guerrero et al., IEEE Trans. Ind. Electron. 60(4), 1263 (2013). A static synchronous compensator (STATCOM) in grid-connected microgrid was introduced to improve voltage sags/swells and unbalance. A model has been developed to study the impact of power sharing controllers and delays in microgrid stability. See A. Kahrobaeian and Y. a.-R. I. Mohamed, IEEE Trans. Power Electron. 30(2), 603 (2015). The effectiveness of the proposed controller was presented through comparative simulation and experimental results. Advanced control techniques have been reviewed, including decentralized, distributed, and hierarchical control of grid-connected and islanded microgrids that consider stability. See J. M. Guerrero et al., IEEE Trans. Ind. Appl. 60(4), 1254 (2013). For large scale energy storage/wind penetration, cyber protection and other stability and power sharing analysis techniques for droop control for transmission systems can be included. See A. Di Giorgio et al., Real Time Optimal Power Flow Integrating Large Scale Storage Devices and Wind Generation, 23rd Mediterranean Conference on Control and Automation, MED 2015; A. DiGiorgio et. al., On the Optimization of Energy Storage System Placement for Protecting Power Transmission Grids Against Dynamic Load Altering Attacks, 25th Mediterranean Conference on Control and Automation, MED 2017; and D. Zonetti et al., IEEE Trans. Control Netw. Syst. PP(99), 1 (2017).
Today's grid model is based on excess generation capacity (largely fossil fuel), static distribution/transmission systems, and essentially open loop control of power flow between sources and loads. Research investments in grid modernization and microgrids are presently being made by the Department of Energy, Department of Defense, and others. See H. R. Baghaee et al., “A Decentralized Power Management and Sliding Mode Control Strategy for Hybrid AC/DC Microgrids including Renewable Energy Sources, accepted for publication in IEEE Trans. Ind. Informat. (2017); E. Unamuno and J. A. Barrera, J. A., Renew. Sust. Energy Rev. 52, 1123 (2015); J. M. Guerrero et al., IEEE Trans. Ind. Electron. 60(4), 1263 (2013); A. Kahrobaeian and Y. a.-R. I. Mohamed, IEEE Trans. Power Electron. 30(2), 603 (2015); J. M. Guerrero et al., IEEE Trans. Ind. Appl. 60(4), 1254 (2013); W. W. Weaver et al., Control Eng. Pract. 44, 10 (2015); F. Luo et al., A Generalized Droop-Control Scheme for Decentralized Control of Inverter-Interfaced Microgrids, in IEEE International Symposium on Circuits and Systems, 2013, pp. 1320-1323; and W. W. Weaver et al., Int. J. Electr. Power Energy Syst. 68, 203 (2015). Other approaches have been developed that optimize distributed energy systems to improve efficiency of the energy resources. See M. Di Somma et al., Energy Convers. Manage. 103, 739 (2015).